Secondary batteries are employed in electrically powered vehicles, in particular electric vehicles and hybrid electric vehicles, in order to be used to supply electrical power to electrical drive systems of the motor vehicle.
Conventional battery systems for electro-mobility applications comprise a hard-wired interconnection of battery cells without cell electronics.
In new types of battery systems, while a motor vehicle of this type is running, the output voltage of the secondary battery is varied according to the load currently applied to the secondary battery. For this purpose, a secondary battery comprises a multiplicity of battery cells connected together electrically in series, with the output voltage currently produced by the secondary battery defined by the current number of battery cells connected together electrically in series and by their states of charge. Battery cells that are not needed for generating a desired output voltage are shunted.
The output voltage of a secondary battery is controlled by enabling or disabling, i.e. shunting, individual battery cells in set time intervals using cell electronic units assigned to the individual battery cells. In each of these time intervals, a number of battery cells are enabled, i.e. activated, which number is the number currently needed to produce a required setpoint output voltage.
Enabled, or activated, battery cells can be introduced into a series circuit of battery cells by means of their cell electronic unit with a positive polarity, i.e. in a positive orientation, or with a negative polarity, i.e. in a negative orientation, with respect to the output voltage taken from a secondary battery. Disabled battery cells are electrically isolated from the series circuit, which is usually achieved by electrically connecting together connecting terminals of the cell electronic units assigned to each of the disabled battery cells, thereby shunting these battery cells.
It is known for the purpose of controlling the output voltage of a secondary battery to activate battery cells according to the corresponding state of charge and other state parameters of the battery cells. A relevant cell state can be described by a quality factor, which is defined using one or more characteristics such as, for instance, the state of charge (SOC), the state of health (SOH) or similar properties of a battery cell, is determined for each battery cell during operation of a secondary battery, and is taken into account in the open-loop and/or closed-loop control of the output voltage of the secondary battery. For example, battery cells having a good state of charge and health can be activated more frequently than battery cells having a poor state of charge and health.